Discovery of Cyanobacterial Natural Products Containing Fatty Acid Residues**

Abstract

In recent years,extensive sequencing and annotation of bacterial genomes has revealed an unexpectedly large number of secondary metabolite biosynthetic gene clusters whose products are yet to be discovered. Fore xample, cyanobacterial genomes contain avariety of gene clusters that likely incorporate fatty acid derived moieties,b ut for most cases we lack the knowledge and tools to effectively predict or detect the encoded natural products.H ere,w ee xploit the apparent absence of af unctional b-oxidation pathway in cyanobacteria to achieve efficient stable-isotope-labeling of their fatty acid derived lipidome.W es how that supplementation of cyanobacterial cultures with deuterated fatty acids can be used to easily detect natural product signatures in individual strains.T he utility of this strategy is demonstrated in two cultured cyanobacteria by uncovering analogues of the multidrug-resistance reverting hapalosin, and novel, cytotoxic, lactylate-nocuolin Ah ybrids-the nocuolactylates.

Fischerazoles A-C, cyanobacterial polychlorinated lipids featuring fatty acyl chain rearrangement

“…After filtering out mass features presumably corresponding to primary metabolites, this analysis led to the identification of 124 labeled positive-mode MS features resulting from incorporation of deuterium atoms. 21 Among these, a few exhibited d7 and d6 incorporation (Fig. 1A) and isotopic patterns consistent with multiple halogenations.…”

“…Discovery of the fischerazoles. In our previous study, 21 we supplemented Fischerella sp. PCC 9431 with pulses of d11-hexanoic acid (d11-C6) and carried out LC-HRESIMS comparative analysis with a non-supplemented culture.…”

“…PCC 9431. 21 Here, we report the detection, in this same cyanobacterium, of a series of additional metabolites showing mass shifts for perdeuterated fatty acid incorporation. The compounds were isolated and their structures elucidated as extensively modified linear lipopeptides, which we named fischerazoles A-C (1)(2)(3).…”

“…18 We have recently developed a BGC-agnostic metabolomics method aimed at the discovery of cyanobacterial natural products containing fatty-acid derived moieties. 21 The method employs supplementation of cyanobacterial cultures with perdeuterated hexanoic acid. Cyanobacteria do not appreciably degrade exogenously supplemented fatty acids and instead elongate them and incorporate them into a wide range of metabolites.…”

“…Cyanobacteria do not appreciably degrade exogenously supplemented fatty acids and instead elongate them and incorporate them into a wide range of metabolites. 21,22 This method exploits this peculiarity to detect mass features that are shifted in mass spectra from cultures receiving perdeuterated fatty acid supplementa-tion. For example, we used this method to discover several hapalosin analogues from Fischerella sp.…”